I’ve been working on personal scripts to remux files and fix Plex playback issues. During this process, I built a diagnostic script that might help identify problems in video files causing Plex playback issues.
These are work-in-progress scripts, but they could help someone troubleshoot problematic video files:
https://github.com/MrMcDan/DansPersonalPlexRemuxScript
Specifically, check out the Get-PlexVideoInfo.ps1 script for video diagnostics.